Rise in Autism Diagnoses Could Be a Result of Reclassification

We know that the number of autism diagnoses continues to rise. In 1975, scientists estimated that one child in 5,000 has autism spectrum disorder (ASD). By 2002, that had changed to 1 in 150 and today it is 1 in 68. What has caused this very significant increase? Some have theorized that a better understanding of autism and a greater awareness plays a large part in why many more children are diagnosed with ASD today than they were 10, 20 or 30 years ago. Some people that these factors, along with a broadening definition of autism is what has caused the number of diagnoses to spike to what some people refer to as “epidemic level.”

Researchers at Pennsylvania State University looked into the question of why the large increase. They found a different reason: reclassification. Researchers used 11 years of special-education enrollment data for over six million children per year. Their research showed that the number of students enrolled in special education didn’t change significantly. But there was definitely an increase in the number of children diagnosed with ASD - just as there was a decrease in the number of children diagnosed with other intellectual disabilities. In other words, the children were reclassified as ASD instead of other disabilities.

Under the Individuals with Disabilities Education Act (IDEA), there are 13 categories children can be placed into.Some of the categories include: ASD, intellectual disability, emotional disturbance, other health impairment, specific learning disabilities. While symptoms of some of these can overlap, and children can have more than one disability, each child can only be placed in one category for IDEA.

Researchers looked at data from 2000 and 2010 and found there were three times as many autism diagnoses in 2010 than there were in 2000. But 65 percent of the increase could be attributed to a reduction in the intellectual disability category. The exact number changed according to age - for eight year olds, reclassification could account for 59 percent of the increase but by the age of 15, reclassification could account for 90 percent of the increase.

Besides age, there were differences by state. The researchers noted that some states, California, New Mexico and Texas, did not show a relationship between intellectual disability and autism. They believe that state-specific health policy might make a difference when estimating autism prevalence.

Other concerns when reporting prevalence rates are that those with autism have a high co-occurrence with other neurodevelopmental disabilities and that each person experiences autism differently, which makes diagnosis that much more difficult.

The results of the research was published online in the American Journal of Medical Genetics.